The present invention relates to an apparatus and a method for expanding preforms into containers within a blow mold by means of a pressurised pneumatic medium.
Apparatuses and methods for expanding containers are applied for example in the industry of manufacturing beverage containers, wherein by means of corresponding treatment systems, inter alia, a preform primarily made from plastic is blown or expanded within a blow mold into a corresponding container that is also made from plastic.
To this end, a corresponding preform is introduced into an inner region of a blow mold that is usually designed in two parts, which blow mold has at least one cavity in the inner region thereof, which is used for shaping the later expanded container. The blow mold principally surrounds the preform over the entire circumference thereof, at least around the bottom area thereof, and the mouth area of the preform, which has a corresponding integral or cut-in internal or external thread, can at least partially protrude out of the blow mold or is not introduced into the blow mold at least in the region of the cavity, so that an expansion and in particular a deformation of the mouth area of the preform during the expansion process thereof is avoided.
The preform is blow molded or stretch blow molded into an expanded container by means of a blow nozzle that can be attached in particular to a mouth area of the preform, through which blow nozzle a pressurised pneumatic or gaseous, flowable medium such as a sterilisation gas or air is introduced into the inner region of the blow mold and thus into the inner region of the container to be expanded or the preform to be expanded.
In one embodiment, a stretch rod is additionally moved from an inlet of the blow mold, which may be located in the region of the mouth area of the preform, up to a bottom area of the blow mold and correspondingly of the continuously expanding container, and to this end the movement is carried out, depending on the positioning or the orientation of the blow mold, substantially along a longitudinal axis of the container and consequently substantially in a vertical or perpendicular direction in relation to the horizontal plane.
However, it is also possible for the blow mold (including the blow nozzle) to move together with the preform correspondingly to be expanded in the direction of the stretch rod and/or the blow nozzle in such a way that as a result of the movement of the blow mold itself, which is carried out in a manner comparable to the movement of the stretch rod substantially in a direction that is normal or perpendicular to the horizontal plane, the stretch rod is accordingly moved through the inner region of the preform to be expanded, so that the introduced pressurised air can be applied substantially uniformly over the inner regions of the preform, as a result of which a deformation of the wall and bottom areas is caused, which is necessary for the expansion of the preform.
However, it is also conceivable that both the stretch rod and/or the blow nozzle as well as the blow mold itself move towards each other and/or away from each other at respectively defined speeds during the expansion process of the preform.
The expansion process of the preform into a container is merely one out of a multiplicity of possible treatment processes of the preform or of the container itself. Accordingly, within an entire system for treating containers, a preform can be treated by way of preheating, heating, disinfecting, drying and/or expanding or blow molding or stretch blow molding, whilst an expanded container can be treated for example using the treatment steps of disinfecting, drying, filling, labelling, sealing with container caps and/or packaging.
The blow molds needed for expansion may be arranged at substantially identical distances from each other on a transport element, such as for example a transport wheel or a star wheel, and are consequently moved by the rotation of the wheel about the central rotation axis thereof also correspondingly at a defined speed about this axis of rotation.
Thus, the preforms are also transported along a specifiable transport path that is orientated in particular perpendicular to the direction of movement of the blow nozzle and/or of the stretch rod and/or of the blow mold.
In one embodiment, the preforms or containers to be expanded are supplied using at least one further transport unit, namely a feed transport unit of the transport unit for the blow molds, and this feed transport unit for the preforms to be expanded is for example a transport belt or a transport wheel. Correspondingly, the expanded containers are taken over from the blow mold transport unit by means of at least one corresponding discharge transport unit and are fed for example to a subsequent treatment station such as for example a disinfection system or a filling system for filling the containers. The containers to be expanded are transferred in the transfer areas between the feed transport unit and the blow mold transport unit or the blow mold transport unit and the discharge transport unit, respectively.
During the expansion process of the preform to be expanded within the blow mold, high blow pressures of for example approximately 35 to 40 bar are used, in particular in order to be able to ensure that the plastic of the preform or the wall of the preform is expanded or deformed in such a way that the latter is inserted or pressed into all of the defined regions of the cavity of the blow mold, so that a container expanded in the manner as defined can be produced. The blow pressure required for this is here dependent, inter alia, on the composition of the plastic, the heating of the preform, the wall thickness of the preform etc.
The generation of the blow air or pressurised air necessary for the expansion of the preform is known to require a lot of energy, in particular also because of the waste heat that is generated in the compressor that compresses the blow air up to a defined pressure. In the case of high-pressure compressors, the waste heat developed is normally discharged to the external environment of the system via a correspondingly provided cooler, in order to avoid for example overheating of the compressor and thus damage to the latter.